Plastic composition and bowling pin made thereof



United States. Patent I O 3,251,598 PLASTIC COMPOSITION AND BOWLDIG PIN MADE THEREOF Robert F. Craig and Robert J. Martinovich, Bartlesville, Okla, assignors to Phillips Petroleum Company, a

corporation of Delaware Filed Mar. 13, 1961, Ser. No. 95,091 11 Claims. (Cl. 273-82) This invention relates to a novel plastic composition and an article of manufacture made thereof, namely a bowling pin. i

In the last decade or so there has been a rapid increase in the number of bowling establishments in this country due to the Widespread public interest and participation in the sport of bowling. Along with this there have been proposed, patented, and evalulated a number of different materials as substitutes for some or all of the wood now generally used in \bowling pins in an attempt to satisfy the demand for a more durable, cheap, and useful bowling pin having a longer life.

At the present time, all bowling pins approved by the American Bowling Congress are constructed of hard maple, some of which are coated with lacquer or a thin layer of plastic. While these wooden bowling pins have enjoyed long and widespread use, they do have a number of shortcomings. The scorability of these hard maple bowling pins is not uniform, but rather varies over the useful life of the pin; new pins (i.e., less than 300 lines) have low scorability, and as the pins get older this scorability tends to increase. In order to obtain maximum pin life for such wooden bowling pins it is common to rest the pins by taking them out of service. after every 300-500 lines of service, during which time the wood fibers reform to a degree and enable the bowling lane proprietor to refinish those pins which are Worn, chipped, marred, splintered, or otherwise damaged. The useful life of the average wooden pin is only about 2500 to 3500 lines. Another disadvantage in the use of bowling pins made of hard maple is that there is a shortage of select hard maple, and it is necessary to grade the wooden pins because of variations in the character of the hard maple that is used in making the .pins. Moreover, such variation in the wood means that the densities of the pins made from various grades of hard maple will vary.

To date none of the materials proposed or evaluated as substitutes for the hard maple of the bowling pins has been able to meet the rigid specifications and standards of the American Bowling Congress and gain acceptance. In particular, all-plastic bowling pins made from plastics such as cellulose acetate, cellulose acetate butyrate, styrene, and conventional (low density) polyethylene have been rejected as substitutes because they have proven to be unsatisfactory for a number of reasons; for example, such plastics have proven to be too brittle, too hard,-and some materials cannot be readily and economically fabricated or machined, While others have not been sufiiciently durable and have not been ableto withstand the harsh treatment encountered in automatic pin setting equipment and upon repeated impact by bowling balls.

Accordingly, an object of this invention is to provide a novel plastic composition. Another object is to provide as a new article of manufacture a bowling pin made of a novel plastic composition, the properties of which make it ideally suited for the fabrication of bowling pins therefrom. Another object is to provide a bowling pin made of a novel plastic composition, which bowling pin is durable, has a relatively long useful life, has a high and uniform scorability, a desirable coefficient of friction, and high impact strength, and other properties which make it especially suitable as a-substitute for the hard Patented May 17, 1966 maple of bowling pins now generally used. Other objects and advantages of this invention will become apparent to those skilled in the art from the following discussion, appended claims, and accompanying drawing which illustrates'in the single figure an elevational view in half-section of a prefrred embodiment of the improved bowling pin of this invention.

The novel plastic composition of this invention, which I is especially suited in fabricating an improved bowling 'cyclohexane and methylcyclopentane.

pin, broadly comprises about 80 to 90 weight percent of a copolymer of ethylene an l-butene having a melt index (hereinafter defined) of 0.3 to 1.2 and about 20 to 10 weight percent of an isobutylene polymer such as polyisobutylene or, preferably, a copolymer of isobutylene and a conjugated diene such as isoprene or 1,3-butadiene. As will be established in detail by the examples of this specification, bowling pins made from said novel plastic composition have uniform scorability throughout the life of the pin, and said pins have a useful life which is far greater than that of wooden pins made of hard maple. Further, the bowling pins of this invention have a greater ability to withstand impact, require a minimum of maintenance, they can be fabricated in an efiicieut and economical manner, and their use eliminates the grading and sale of odd lot pins fabricated from hard maple.

The copolymer of ethylene and l-butene used in accordance with this invention has a density (hereinafter defined) of from 0.948 to 0.952; this represents an incorporation of from 1.5 to 1.0 weight percent, respectively, based on total monomers, of the l-butene comonomer into the copolymer molecule. Preferably, the density of the copolymer is approximately 0.950 to 0.951. The melt index of these copolymers is in the range of approximately 0.3 to 1.2. Copolymers of this type are preferably prepared by the copolymerization of a major amount of ethylene and a minor amount of l-butene in the presence of a catalyst consisting essentially of chromium oxide supported. on a silica-alumina composite, the catalyst containing at least 0.1 weight percent chromium in the hexavalent state. The total chromium content of the catalyst is generally, though not necessarily, within the range of 1 to 10 weight percent of the total catalyst. The copolymerization is frequently carried out at a temperature within the range of from about 230 to 300' F. Ordinarily, the copolymerization is conducted in the presence of a hydrocarbon diluent which is liquid and inert under the reaction conditions. Generally, this diluent is a naphthene or a paraflin hydrocarbon having from 3 to 12 carbon atoms per molecule. Examples of such hydrocarbons are normal pentane, normal hexane, 2,2,4-trimethylpentane, The catalyst is preferably used as a granular suspension thereof in the diluent. Further details of this process can be obtained by a reading of US. Patent 2,825,721 which was issued March 4, 1958, to J. P. Hogan and R. L. Banks. Other suitable copolymers, though less preferred than those tetrachloride, a mixture of ethylaluminum chloride with titanium tetrabutoxide, and similar catalysts, discussed in more detail in US. Patent 2,846,427, issued August 5, 1958, to R. A. Findlay, and US. Patent 2,826,447, issued March 18, 1958, to Gene Nowlin and H. D. Lyons.

A number of copolymer of ethylene and l-butene, made in the manner. described, which are useful in the practice of this invention are set forth in Table I together with certain physical properties.

The density referred to herein, is determined by ASTM Method D 15 05-57T. Ethanol and water were used as the suspending liquids. The samples used for density determination are prepared by compression-molding molten pellets of the ethylene polymer to form 'a slab about 6 inches square and 19, to inch thick. The slabs are molded at 20,000 p.s.i. and 330 F. The heat is then turned off. Tap water is circulated through the mold cooling system. The slab is cooled to 200 F. at the rate of 25 F. per minute, and then to 150F. as rapidly as possible by increasing the flow rate of the cooling water. The slab is then removed from the mold and allowed to stand for 24 hours at room temperature. Small pieces of the slab, e.g. about A inch squares, are cut off for the density determination. These pieces are examined to be sure that they have no surface pits or other features which might occlude or entrap air when immersed in liquid. 7

The melt index, as referred to herein, is determined in accordance with ASTM Method D 1238-52T.

minor amount of the isobutylene polymer. Generally, the amounts of said materials used will be suflicient to provide a blend comprising 80 to 90 Weight percent of the ethylenel-butene copolymer and about 20 to weight percent of the isobutylene polymer. While the plastic composition of this invention'can consist essentially of just these two polymeric materials, it is also within the scope of this where used) in a Banbury mixer (Without prior heating) and mixing the materials in said mixer for a period of time and at a temperature sufficient to obtain a homogeneous blend, e,g., 5 to 7 minutes to a temperature of about 300 to-350 F., preferably about 320 F. The resulting blend- TABLE I Ethylene-l-butene copolymer Property Test A B C Density, gms./cc ASTM D 150557T 0.950 0. 950 0, 950 Melt index ASTM D 123857T 0.3 0.5 1, 2 Environmental stress cracking re- ASTM D 169359T 350 175 55 sistanee, F hrs.

Tensile strength, in./min., p.s.i ASTM D 63858T 3,800 3, 800 3, 800 Elongation, 20 in./min.,pereent ASTM D 638--58T 70 5 40 Impact strength, ft. lbs/in. notch ASTM D 25656.' v4. 0 2.0 1. 0 Vicat softening temp., F ASTM D 1525-58T 255 255 255 Brittleness temp., F ASTM D 74657T -18O 180 -180 Stiffness, p.s.i ASTM D 7 758 115,000 115,000 115, 000 Hardness- Shore D 67 7 as isoprene, butadiene, dimethylbutadiene, piperylene,.

hexadiene-1,3, and the like. The preparation of these isobutylene polymers by low-temperature catalytic polymerization is Well known in the art and need not be described herein in detail. One useful method of preparing polyisobutylene is that disclosed in U.S. Patent 2,240,582. These polyisobutylenes will have varying molecular weights, for example in the range of 1,000 to 1,000,000 and are characterized as rubbery solids which are tough, elastic materials having an elastic memory. These polyiso'butylenes and a method of molecular Weight determination (Staudinger Viscosity Method) are described in an article by Thomas et al. in Industrial and Engineering Chemistry, 32, p. 299 (1940). The preparation of the rubbery copolymers of isobutylene and conjugated dienes is also well known, and U.S. Patents 2,356,128, 2,356,129 and 2,356,130 disclose their preparation. These copolymers are known in the art as butyl rubbers. Butyl rubbers with Mooney viscosities of 30 to 80, preferably 60 to 75, can be used in the plastic composition of this invention. A useful commercial product of this type which can be used in this invention is Enjay Butyl 268, which is a copolymer of isobutylene and 1.5 weight percent isoprene having an average mole percent unsaturation of 1.4 and a Mooney viscosity of 71. Other examples of butyl rubber known in the art are GR'I, Butyl A, Butyl C, and Flexon.

The plastic composition used in making the bowling pins of this invention can be prepared by blending or mixing a major amount of the ethylene-l-butene copolymer and a ed mixture can be sheeted and chopped into small particles. The comminuted blend can then be used to fabricate the bowling pin by means of injection molding, compression molding, or other techniques of fabrication well known in the art.

A representative plastic composition comprising about 86 Weight percent ethylene-l-butene copolymer (B in Table 1) and about 14 weight percent butyl rubber (Enjay Butyl 268) useful in preparing the bowling pin of this lnvention is set forth in Table II together with the physical properties which makes it especially well suited for this application.

TABLE II Property Test Value Density, gins/cc ASTM D 1505-57T 0. 948 Meltmdex ASTM D 123857'I 0.45 Environmental stress cracklng resist- ASTM D 169359T 480 anee, F50 hrs. Tensile strength, 20 in./min., p.s.i ASTM D 63858T 2, 800 Elongation, 20 1n./min., percent ASTM D 638-58T 160 Impact strength, ft. lbs. in noteh ASTM D 25656 12 Vrqat softening temp. F ASTM D 1525-58T 244 Brlttleness temp, F ASTM D 746-57T..- 110 Stlfihess, p.s.i ASTM D 74758T 64, 000 Hardness Shore D 65 Ooeflieient of friction (kinetic) 0.36

The plastic composition of this invention has physical properties which make it especially well-suited for use in composition is attached at one end to a weight or sled of known weight (e.g., 4.3 lbs.) which is aflixed to a wire that is passed over a pulley and attached to one of the force exerting (or pulling) members of the testing a Table IV, together with their coefficient of friction and hardness properties.

TABLE III machine, so as to pull or slide the second sheet of plastic 5 Property Test Value over the first sheet in the stationary bed. The pounds of fldrce (disclounti)ng the static frilcltidln betwegnhthe two {L g g [L950 s eets o pastic necessary to pu t e secon s eet over 9 J 0X the first sheet, as indicated by the testing machine dial, stress cm mg I ASTMD 1693 591 20 Tensile strength, 20 in./min. p.s.i ASTM D 638-58T..- 3,800 13 demrmmed and this Value lshdlvlded i g of Elongation, in./n1in., percent ASTMD 638-58T.-- the sled aflixed to the seclpndls eet to give t e coe cient {7mp?ct? engfl%[t, 1bS i n,n0te11 fig%:%11g256-56. f" 0.8 t i iCQHSO ening emu, 1525-58 255 of fnctlon (kmetl?) o t P m comgosinoil l fi Brittlemess temp "F ASIMD 74657T 16O The accompanying drawing illustrates in ts sing e gur e Stiffness ASTM D 115,000 a preferred embodiment of the novel bowling pm of this Shm D 67 invention. Referring to that drawing, the bowling pin 15 TABLE IV Ingredients, weight percent Type of I Coe'fiicient Hardness, composition Ethylene- Glyceryl of friction, Shore D l-bntene Butyl rikinetic copolymer rubber stearate (Table III) comprises an elongated main body 1 with a neck portion defined by the smallest cross sectional area and a ball impact portion defined by the largest cross sectional area, head cap 2, and base cap 3, which elements can be heat sealed by a butt weld at 5 and 6 to form a hollow 7. The pin portions are formed from the novel plastic composition disclosed herein, preferably by injection molding. The pin further comprises a base 8 and base lockingpin 9 having suitable key slots 10 therein. The base 8 can be provided with one or more lugs where it abuts the lower end of base cap 3, and locking pin 9 can be turned to to secure this lower pin assembly together. These 40 Pins made of the compositions shown in Table IV upon 30 subjecting the same to bowling alley service were found to have unsatisfactory durability, in that they exhibited excessive neck fracture and, in the case where glyceryl tristearate wax was incorporated in the composition, delamination of components, the average life of these pins being less than 3000 lines. All of the compositions used in making these pins are outside the scope of this invention, but se-rve here for purpose of comparison.

Complete sets of regulation size bowling pins were made of the compositions shown in Table V and also subjected to bowling alley service.

1 Table III.

2 B in Table I.

latter elements 0, 10 can also be formed of the novel plastic composition of this invention or other plastic materials, such as cellulose butyrate. This preferred'e'mbodiment has proven to be extremely durable with a pin life in excess of 4300 lines 'without any fracture and with 60 a high and uniform scorability. It should be understood, of course, that this invention is not to be limited to this embodiment, since this aspect of invention broadly resides in a bowling pin of the plastic composition described without limiting the same to any specific'design.

Further objectsand advantages of this invention will now be illustrated by the following examples, but it should be understood that the various materials, properties, additives, etc., set forth in these examples should not be construed to limit unduly this invention. 70

Examples 268). These bowling pin compositions are shown in 75 Pins made of composition 9 according to this invention were found to be extremely durable with a life in excess of 4300 lines, while pins made of composition 8 (with a low coeflicient of friction) exhibited delairiination of ingredients, and pins made of composition 7 were not durable because of neck failure and had an average life of less than 2600 lines.

In the course of our investigations, we have found that bowling pins made entirely of low pressure (high density) polyethylene homopolymer were not durable in that they exhibited neck failure, e.g., after 350 lines. Other pins made only of the copolymer of ethylene and l-butene (A in Table 1), although durable, were too hard (69-71 Shore D hardness) and had low scorability characteristics. We have also found that pins made of about 70 Weight per-cent of a copolymer of ethylene and l-butene (B in Table I) and about 30 weight per-cent polyisobutylene (Vistanex) had a high coefficient of friction (0.632) and low hardness (56-58 Shore D), these pins exhibiting unsatisfactory scorability characteristics.

7 The above examples establish that bowling pins made of the novel composition disclosed herein are durable, have long life, and desirably high and uniform scorability. Said examples further establish the criticality in blending 80 to 90 weight percent of a copolymer of ethylene and l-butene, with melt indexes of 0.3 to 1.2, and 20 to percent of a polymer of isobutylene, to provide a blended composition useful in making bowling pins.

Various modifications and alterations of this invention will become apparent to those skilled in the art from the foregoing discussion and accompanying drawing, and it should be understood that this invention is not to be unduly limited to that set forth herein for illustrative purposes.

We claim:

1. A bowling pin comprising an elongated main body, head cap, and base cap elements each molded from a plastic composition comprising about 80 to 90 weight percent of a copolymer of ethylene and l-butene having a melt index in the range of about 0.3 to 1.2, and about 10 to 20 weight percent of a polymer of isobutylene selected from the group consisting of polyisobutylene and a copolymer of isobutylene and a conjugated diene having 4 to 8 carbon atoms per molecule.

2. A bowling pin comprising an elongated main body, head cap, and base cap elements each molded from a plastic composition comprising about 80 to 90 weight percent of a copolymer of ethylene and l-butene having a melt index in the range of about 0.3 to 1.2, and about 10 to 20 weight percent of polyisobutylene.

3. A plastic composition comprising about 80 to 90 weight percent of a copolymer of ethylene and l-butene having a melt index in the range of about 0.3 to 1.2, and about 10 to 20 weight percent of a copolymer of isobutylene and a conjugated diene having 4 to 8 carbon atoms per molecule.

4. A plastic composition comprising about 80 to 90 weight percent of a copolymer of ethylene and, l-butene having a melt index in the range of about 0.3 to 1.2, and about 10 to 20 weight percent of a copolymer of isobutylene and isoprene.

5. A plastic composition comprising about 86 weight percent of a copolymer of ethylene and l-butene with a melt index of about 0.5, and about 14 weight percent of a copolymer of isobutylene and a conjugated diene having 4 to 8 carbon atoms per molecule, said plastic composition having a Shore D hardness of about 61 to 67 and a coeificient of friction (kinetic) of about 0.36 to 0.40.

6. A plastic composition consisting essentially of about 80 to 90 weight percent of a copolymer of ethylene and l-butene having a melt index in the range of 0.3 to 1.2 and a density in the range of 0.948 to 0.952, and about 10 to 20 weight percent of a copolymer of isobutylene and isoprene.

7. A bowling pin comprising an elongated main body, head cap, and base cap elements each molded from a plastic composition consisting essentially of about 80 to 90 weight percent of a copolymer of ethylene and l-butene having a melt index in the range of 0.3 to 1.2 and a density in the range of 0.948 to 0.952, and about 10 to 20 weight percent of a copolymer of isobutylene and isoprene.

8. A plastic composition consisting essentially of about 86 weight percent of a copolymer of ethylene and l-butene with a melt index of about 0.5 and a density of about 0.948, and about 14 weight percent of a copolymer of isobutylene and about 1.5 weight percent isoprene with an average mole percent unsaturation of about 1.4 and a Mooney viscosity Of about 71, said plastic composition 8 having a Shore D hardness of about 61 to 67 and a coefficient of friction (kinetic) of about 0.36 to 0.40.

9. A bowling pin comprising an elongated main body with a neck portion defined by the smallest cross sectional area and a ball impact portion defined by the largest cross sectional area of said main body, a head cap surmounting said main body, and a base cap depending from said main body, said head cap, main body, and base cap being secured at their adjacent portions to form a hollow, said head cap, main body, and base cap being made of a plastic composition comprising about to weight percent of a copolymer of ethylene and l-butene having a melt index in the range of about 0.3 to 1.2, and about 10 to 20 weight percent of a polymer of isobutylene selected from the group consisting of polyisobutylene and a copolymer of isobutylene and a conjugated diene having 4 to 8 carbon atoms per molecule.

10. A bowling pin comprising an elongated main body with a neck portion defined by the smallest cross sectional area and a ball impact portion defined by the largest cross sectional area of said'main body, a head cap surmounting said main body, and a base cap depending from said main body, said head cap, main body, and base cap being secured at their adjacent portions to form a hollow, said head cap, main body, and base cap being made of a plastic composition comprising about 86 weight percent of a copolymer of ethylene and l-butene with a melt index of about 0.5, and about 14 weight percent of a copolymer of isobutylene and a conjugated diene having 4 to 8 carbon atoms per molecule.

11. A bowling pin comprising an elongated main body with a neck portion defined by the smallest cross sectional area and a ball impact portion defined by the largest cross sectional area of said main body, a head cap surmounting said main body, and a base cap depending from said main body, said head cap, main body, and base cap being secured at their adjacent portions to form a hollow, said head cap, main body, and base cap being made of a plastic composition consisting essentially of about 86 weight percent of a copolymer of ethylene and l-butene with a melt index of about 0.5 and a density of about 0.948, and about 14 weight percent of a copolymer of isobutylene and about 1.5 weight percent isoprene with an average mole percent unsaturation of about 1.4 and a Mooney viscosity of about 71.

References Cited by the Examiner UNITED STATES PATENTS 2,369,471 2/ 1945 Latham 26045.5 2,684,504 7/1954 Sell 27382 XR 2,791,576 5/1957 Field et al. 26045.5 2,825,721 3/1958 Hogan et a1 26094.9 2,830,919 4/1958 Schatzel 26045.5 3,025,061 3/1962 Ernst et al. 3,044,777 7/ 1962 Friedman 273-82 3,048,400 8/1962 Friedman 27 382 3,074,616 1/ 1963 Martinovich et al.

26089 XR 3,169,766 2/1965 Ernst 273-82 FOREIGN PATENTS 597,760 5/1960 Canada.

OTHER REFERENCES De Coste et al.: Ind. Eng. Chem., vol. 43, pp. 117-121, 1951.

RICHARD C. PINKHAM, Primary Examiner.

LOUIS R. PRINCE, Examiner. 

2. A BOWLING PIN COMPRISING AN ELONGATED MAIN BODY, HEAD CAP, AND BASE CAP ELEMENTS EACH MOLDED FROM A PLASTIC COMPOSITION COMPRISING ABOUT 80 TO 90 WEIGHT PERCENT OF A COPOLYMER OF ETHYLENE AND 1-BUTENE HAVING A MELT INDEX IN THE RANGE OF ABOUT 0.3 TO 1.2, AND ABOUT 10 TO 20 WEIGHT PERCENT OF POLYISOBUTYLENE.
 4. A PLASTIC COMPOSITION COMPRISING ABOUT 80 TO 90 WEIGHT PERCENT OF A COPOLYMER OF ETHYLENE AND 1-BUTENE HAVING A MELT INDEX IN THE RANGE OF ABOUT 0.3 TO 1.2, AND ABOUT TO 10 TO 20 WEIGHT PERCENT OF A COPOLYMER OF ISOBUTYLENE AND ISOPRENE. 